1. Field of the Invention
The present invention relates to an engine cooling structure used in a water-cooled engine for a motorcycle or the like. More particularly, the present invention relates to an engine cooling structure including a water pump for pumping coolant to a water jacket of the engine, and a thermostat which switches channels through which the coolant is routed on its way back from the water jacket to the water pump, according to the temperature of the coolant.
2. Background Art
Water cooled engines are well known. One known engine cooling structure used in a water-cooling engine has a configuration including: a water pump pumping coolant to the water jacket of the engine; a main circulation channel for returning the coolant which has passed through the water jacket to the water pump through a radiator; a bypass channel for returning the coolant which has passed through the water jacket to the water pump not through the radiator; and a thermostat which switches the channel for returning the coolant to the water pump between the main circulation channel and the bypass channel according to the temperature of the coolant, the thermostat being provided at a position close to the water pump.
In addition, in this kind of an engine cooling structure for a motorcycle, one structure has been proposed in which the water pump is disposed on a side of a cylinder head of the engine on the same axis as the cam shaft, and in which the thermostat is disposed at a position close to the water pump with the axis direction thereof directed orthogonal to the axis direction of the water pump. This engine cooling structure is disclosed, for example, in Japanese Patent Laid-Open Publication No. 2002-021562.
However, the above-described cooling structure is problematic since, by mounting the cooling structure at this location, the cooling structure projects outwardly from the vehicle body. The projection amount on the side of the cylinder head becomes large, and the degree of freedom of layout around the cylinder head therefore decreases.
In order to solve such a problem, it has been suggested to dispersedly arrange component parts, such as the water pump and the thermostat, around a crankcase.
However, if the positions of the water pump and the thermostat are merely moved to the periphery of the crankcase, the distance between the water pump or the like and the water jacket becomes large, and the piping construction installed around the engine becomes complicated. Thus, a new problem arises that the number of assembly steps for installing piping increases. In addition, it is conceivable that, as a result of laying out the exhaust pipe so as to avoid interference between component parts of the vehicle body such as the exhaust pipe and the water pump, the exhaust pipe affects the banking angle of the vehicle body.
An object of the present invention concerns solving the above-described problem. An engine cooling structure is provided which can increase the degree of freedom of layout around a cylinder head by keeping the projection amount on a side of the cylinder head small, does not cause complication in the piping construction, and can achieve reduction in the number of assembly steps. Moreover, an object of the present invention is to provide the engine cooling structure in which the water pump and the like do not interfere with the layout of the exhaust pipe, and which makes it easy to arrange the exhaust pipe in such a manner that the exhaust pipe does not affect the banking angle of the vehicle body.